The present invention relates generally to thin film magnetoresistive transducers, and more particularly to a megnetoresistive transducer which is suitable for reproduction of signals recorded in narrow tracks of an associated magnetic recording medium.
Magnetoresistive elements are known to exhibit change in resistivity in response to changes in an externally applied magnetic field. However, when utilized to detect signals recorded on narrow tracks, having a width on the order of 25 .mu.m or less, they suffer from Barkhausen noise due to large demagnetization fields that cause domain wall formation. The latter effects prevent utilization of these magnetoresistive elements in high density narrow track multichannel transducer applications.
Conventional magnetoresistive transducers have sense currents that flow parallel to the easy axis of the magnetoresistive elements, which is parallel to the air bearing surface and perpendicular to the track being read, as described by C. Tsang in Journal of Applied Physics, Vol. 55 No. 6, page 2226 (1984). An arrangement was patented by Yeh et al. in U.S. Pat. No. 4,356,523 entitled "Narrow Track Magnetoresistive Transducer Assembly," in which the sense current is oriented perpendicular to the easy axis direction of the magnetoresistive elements and perpendicular to the air bearing surface. H. Suyama et al. published experimental results for this transducer geometry in IEEE Transactions on Magnetics, Vol. 24, No. 6November 1988, that showed very low Barkhausen noise.
The Yeh patent describes a transducer wherein two closely spaced magnetostatically coupled magnetoresistive elements are arranged with their respective planar surfaces in parallel. A nonmagnetic insulating material is interposed between the elements to prevent ferromagnetic exchange coupling. Sense current flows simultaneously through both elements in the same direction and perpendicular to the easy axis of the magnetization. In response to signal fields applied in parallel with the sense current flow, demagnetization components in the easy axis direction cancel. The output signal of the transducer is indicated to be independent of recording track width and free of Barkhausen noise.
The Suyama article indicates that its two laminated magnetoresistive elements provide magnetic flux closure, thus minimizing magnetic pole formation at the edges of the elements and assuring a single domain structure inside the two magnetoresistive elements. This is assured by sense currents that flow in the same direction in the two elements and provide oppositely directed magnetization in the magnetoresistive elements.